Racemic amino acids from the ultraviolet photolysis of interstellar ice analogues

The delivery of extraterrestrial organic molecules to Earth by meteorites may have been important for the origin and early evolution of life. Indigenous amino acids have been found in meteorites-over 70 in the Murchison meteorite alone. Although it has been generally accepted that the meteoritic amino acids formed in liquid water on a parent body, the water in the Murchison meteorite is depleted in deuterium relative to the indigenous organic acids. Moreover, the meteoritical evidence for an excess of laevo-rotatory amino acids is hard to understand in the context of liquid-water reactions on meteorite parent bodies. Here we report a laboratory demonstration that glycine, alanine and serine naturally form from ultraviolet photolysis of the analogues of icy interstellar grains. Such amino acids would naturally have a deuterium excess similar to that seen in interstellar molecular clouds, and the formation process could also result in enantiomeric excesses if the incident radiation is circularly polarized. These results suggest that at least some meteoritic amino acids are the result of interstellar photochemistry, rather than formation in liquid water on an early Solar System body.     

宽带电磁散射特性的Chebyshev逼近分析

将切比雪夫逼近理论应用于目标宽带电磁散射特性分析中,通过求解给定频带的切比雪夫节点并用有限元方法求得各节点处的目标表面场值,实现整个频带内任一频率点目标表面场值的快速预测,使得目标电磁散射特性得到快速分析.这一方法避免了在给定频带内对有限元矩阵的反复计算,大大减少了计算机的内存.     

基于LMDS的小区宽带无线接入网方案设计

针对目前应用于住宅小区中的几种宽带接入技术的不足及为了解决因接入网宽带不足而出现的网络"瓶颈"问题,介绍了近年来受到国内外电信业务经营者普遍重视的一种新兴的宽带无线接入技术--LMDS.对基于LMDS技术的住宅小区宽带无线接入网络进行了设计.该系统可用频带宽,支持话音、数据、图象等双项通信业务,无须架设线路,具有建设速度快、初期投资小、系统扩展性好、受环境制约小、又能满足住宅用户对快速业务的需求.可以预见,LMDS将逐渐成为用于高速多媒体应用的最佳网络接入方案.     

The development of silicate matrix phosphors with broad excitation band for phosphor-convered white LED

This paper briefly reviews the recent progress in alkaline earth silicate host luminescent materials with broad excitation band for phosphor-convered white LED. Among them, the Sr-rich binary phases （Sr, Ba, Ca, Mg）2SiO4：Eu^2＋ and （Sr, Ba, Ca, Mg）3SiO5：Eu^2＋ are excellent phosphors for blue LED chip white LED. They have very broad excitation bands and exhibit strong absorption of blue radiation in the range of 450-480 nm. And they exhibit green and yellow-orange emission under the InGaN blue LED chip radiation, respectively. The luminous efficiency of InGaN-based （Sr, Ba, Ca, Mg）=SiO4： Eu^2＋ and （Sr, Ba, Ca, Mg）3SiO5：Eu^2＋ is about 70-80 lm/W, about 95 %-105% that of the InGaN-based YAG ：Ce, while the correlated color temperature is between 4600--11000 K. Trinary alkaline earth silicate host luminescent materials MO（M=Sr, Ca, Ba）-Mg（Zn）O-SiO2 show strong absorption of deep blue/near-ultraviolet radiation in the range of 370-440 nm. They can convert the deep blue/near-ultraviolet radiation into blue, green, and red emissions to generate white light. The realization of high-performance white-light LEDs by this approach presents excellent chromaticity and high color rendering index, and the application disadvantages caused by the mixture of various matrixes can be avoided. Moreover, the application prospects and the trends of research and development of alkaline earth silicate phosphors are also discussed.     

对国外一种大范围、宽滞回带电压监控器的性能分析和改进

分析进口电压监控器的电路性能 ,发现电压适应范围小、无过流保护、可视性低等设计缺陷及实际应用的局限性 .根据工厂实际供电情况 ,应用常用元件 ,对之进行了改进 ,提高了该产品对电源电压波动的适应性和运行稳定性 .根据进口电压监控器的电路及其实现 ,提出了改进国产欠电压继电器的方法     

Further evidence for small-bodied hominins from the Late Pleistocene of Flores, Indonesia

Homo floresiensis was recovered from Late Pleistocene deposits on the island of Flores in eastern Indonesia, but has the stature, limb proportions and endocranial volume of African Pliocene Australopithecus. The holotype of the species (LB1), excavated in 2003 from Liang Bua, consisted of a partial skeleton minus the arms. Here we describe additional H. floresiensis remains excavated from the cave in 2004. These include arm bones belonging to the holotype skeleton, a second adult mandible, and postcranial material from other individuals. We can now reconstruct the body proportions of H. floresiensis with some certainty. The finds further demonstrate that LB1 is not just an aberrant or pathological individual, but is representative of a long-term population that was present during the interval 95-74 to 12 thousand years ago. The excavation also yielded more evidence for the depositional history of the cave and for the behavioural capabilities of H. floresiensis, including the butchery of Stegodon and use of fire.     

间接紫外吸光光度法测定蔬菜中Vc含量

用I3^-间接紫外吸光光度法测定了11种蔬菜中的Vc含量，并进行了重复实验和回收实验。结果：Vc含量在0．116—0．872mmol／kg之间；重复实验的CV在0．38％--8．31％之间；回收率在92．05％--107．09％之间。该方法的准确度较好，且方法简便，灵敏度可达0．025mmol/kg，可用于新鲜蔬菜中Vc的快速、简易测定。     

Fabrication of double-walled carbon nanotube film/TiO2 nanotube array heterojunctions with length-dependent photoresponse for broad band photodetectors

A novel photodetector based on double-walled carbon nanotube (DWCNT) film/TiO₂ nanotube array (TNA) heterojunctions was fabricated, which exhibited high photoresponse in a broad spectral range. The photoresponse of the detector was dramatically dependent on the length of the TNAs. High photocurrent-to-dark current ratio with a value of 3360 was observed in the visible range by optimizing the lengths of the TNAs. The photosensitive regions could be extended into the near-infrared range. These results reveal that DWCNT film/TNA heterojunctions show potential applications for broad band photodetectors.     

巧解砂岩分类三角图

在充分对比砂岩等边三角形和等腰三角形两种分类方案投点图的基础上,尝试从两种不同的思路对砂岩三角形分类方案投点图计算模型进行了推导,即直线方程推导模型和相似三角形推导模型,提出了更为简单的砂岩分类三角图投点计算模型。该计算模型只与石英和岩屑的含量有关,而与三角图本身的形状(等腰或等边三角形)没有直接的关系。再根据Microsoft Excel所提供的逻辑函数建立了砂岩类型的自动识别模型,使大数据量砂岩的分类统计变得更加准确而快捷。最后通过对大数据量储集砂岩骨架组分的定量实例研究,验证了所建立的砂岩分类自动识别模型,以及砂岩分类三角图投点简化计算模型的良好效果。